Amateur Radio Propagation Guru Says Extended Solar Ebb May Lie Ahead

Amateur Radio propagation and solar phenomena authority Carl Luetzelschwab, K9LA, said in an April 27 webinar, “Are We Headed into Another Maunder Minimum? What Does That Mean for Propagation?” that most solar scientists believe several low solar cycles lie ahead, ushering in periods of diminished HF propagation, especially on the higher bands. Luetzelschwab, who maintains K9LA’s Amateur Radio Propagation Web Site and pens a regular “Propagation” column for NCJ, stopped short of concluding that we’ll experience a Maunder minimum — an extended period of very few or no sunspots. As the Marshall Space Flight Center’s “Solar Physics” web page explains, early sunspot records indicate that the Sun went through an inactive period from about 1645 to 1715 — called the Maunder minimum after the scientist who discovered it — when very few sunspots were observed.

“Right now there’s nothing bulletproof to say we’re heading into a Maunder minimum, so we’re just going to have to wait and see,” Luetzelschwab told the webinar, sponsored by the World Wide Radio Operators Foundation (WWROF). “It sure looks like something inside the sun changed around the peak of Cycle 23. There’s lots of evidence that we’re entering a grand solar minimum. But I don’t think any of the solar scientists are 100 percent sure that we’re going to see a Maunder-type minimum.” A grand solar minimum, he explained, is an extended period of low sunspot activity but not as severe as a Maunder minimum.

Many solar scientists believe that Cycle 24 — the current solar cycle — is the weakest in years, and that this portends even less sunspot activity in the future. Some even have predicted outright that a Maunder minimum is around the corner.

In the hour-long presentation, Luetzelschwab reviewed the conclusions of research published by several solar scientists, raising various scenarios for what might lie ahead in terms of sunspots and related HF propagation. If a Maunder minimum were to occur, he predicted “we’ll probably have some pretty good low-band propagation. Most everybody believes the low bands are better at solar minimum.” But he conceded that a lot of factors come into play when trying to foresee what will happen from one solar cycle to the next and how it will affect radio propagation.

In a period of extremely few sunspots, Luetzelschwab said, we might expect “spotty” F2 layer propagation on 15 meters and “probably 12 and 10 will be noise.” He said that if it’s a Dalton-type minimum, “we’ll probably experience propagation kind of like what we’re experiencing right now in this Solar cycle.” The Dalton minimum, from about 1790 until 1830, was another extended low-sunspot period that was not as severe as the earlier Maunder minimum.

Some of the factors scientists believe could predict solar conditions include “hemispheric asymmetry,” where the number of sunspots in the Sun’s northern and southern hemispheres differ. Prior to solar minima, more sunspots may appear in one solar hemisphere than the other, although Luetzelschwab pointed out that this does not always occur over the course of the solar record. “Cycle 23 had a second peak, because the southern hemisphere sunspots peaked,” he noted.

Another factor is the condition of the Sun’s polar magnetic flux field. “Note that the magnetic field of the sun reverses at solar max,” Luetzelschwab said. He told his audience that the solar polar fields are decreasing, but after the Solar Cycle 23 maximum, “They just did not pick up. They’re pretty low.”

“We need to gather some really good data” over the next 10 years, Luetzelschwab concluded, adding that the additional data will provide evidence one way or the other. “This would cover the decline of Cycle 24 and the ascent of Cycle 25 to maybe get a better idea of what the sun is doing,” he said.

“Are We Headed into Another Maunder Minimum? What Does That Mean for Propagation?” will be posted in the webinar archive on the WWROF website.